Melts are obtained in many industrial chemical processes. For example, large amounts of liquid sulfur arise from what is called the Clauss process in refineries. Various operations are now available for converting the liquid melt to a manageable and solid form. The molten products are converted with an application device to suitable forms such as balls, flakes, pellets or other forms. In some instances, the molten products are converted to homogeneous forms. In other instances, the molten products are converted to homogeneous, very substantially spherical forms (cooling belt plants). In the continuous processes, the industry pays special attention to cleanliness of the conveying devices, which are preferably steel conveyor belts, and good separation of the shaped bodies from the conveying devices, in order that the process can run continuously for prolonged periods. In addition, good meterability of the products and inexpensive and clean packaging of the products are required. More particularly, a homogeneous shape and size of the shaped bodies is important, this requiring good separation of the products from the conveyor belts, in order that these products can be transported further and are meterable accurately at a later stage. If the shape of the melt granules has corners and edges, these can fracture and cause dust to form, particularly in the course of sulfur pelletization. In addition, such bodies are unwanted since they cannot be metered accurately in downstream operations.
Steel belt coolers are a frequently used technology in the solidification of the melts. In the course of this technology, the melt is continuously cooled and solidified. By means of different technologies, it is possible to form a wide variety of different shapes of particular size. Perforated plates are a relatively old technology (see, for example, Aufbereitungstechnik 1970 No. 5, p. 278). These involve conducting a sulfur melt from the Clauss process through one or more perforated plates into a prilling vessel filled with water (see, for example, U.S. Pat. No. 3,637,361).
DE-A 2928401 describes a process for pelletizing sulfur, in which molten sulfur is applied to a metal carrier and cooled until solidification, the application of the molten sulfur to the metal carrier is preceded by application of a composition comprising a solvent, an organic titanate and carboxy-functional siloxanes.
A technology which is widespread nowadays is the solidification of sulfur melts by means of steel belt coolers and the Rotoformer® (Rotoform system), as supplied, for example, by Sandvik Process Systems. This involves supplying the molten sulfur at a temperature of 125° C. to 145° C. to a Rotoformer®, and the latter applies the molten sulfur in droplet form homogeneously to a steel belt, the underside of which is cooled by water, for example by means of spray nozzles, or it is passed through a water bath. In this operation, a good separation of the shaped bodies and homogeneous, very substantially spherical shape of the melt granules is ensured. The principle of these processes is described, for example, in U.S. Pat. Nos. 6,398,989 and 4,279,579, and in the brochures “Sandvik—Ihr Partner in der Schmelzengranulierung”, PS-442/GER 10.2003 and “Sandvik Process Systems—Ihr Partner in industrieller Verfahrenstechnik”, PS-400 GER 2.2011, each published by the Sandvik group (www.smt.sandvik.com).
Especially in the granulation of sulfur by the various processes for producing particular melt granules, for example pellets, it is necessary to use release agents to prevent possible adhesion to steel belts or other conveying devices. In addition, the release agents have a positive influence on the shape of the melt granules, which improves subsequent packaging and reuse (accurate metering). One example of a frequently used release agent is silicone oil. GB 1 537 888 describes the use of silicone oils of viscosity 20-50 cSt from, for example, Dow Corning. This fluid is sold under the DOW CORNING® 200 FLUID, 20 cSt trade name. The release agent is dispersed in the molten sulfur and simplifies pelletization, which is effected on a cooled steel belt. One disadvantage of this technology is that it is necessary to disperse the silicone oil in the sulfur. Since the silicone oil is a liquid and is completely incompatible with water, which is used to cool and clean the steel belts, there are instances of soiling and greasy residues in the plant, which adversely affect the separation of the shaped bodies from the steel belt cooler. An improvement was achieved by the use of silicone oil emulsions. The application of the emulsion by spraying or else dipping of the steel belts eases the process, but silicone residues adhering on the belts cannot be re-emulsified and therefore lead to soiling. A further disadvantage of the emulsions is the stability thereof. Separation of the silicone oil from the aqueous phase frequently occurs at 35° C., which complicates the use of a silicone oil in refineries in hot countries, since the silicone oil frequently separates even in storage or reservoir vessels, or in conveying devices.
The disadvantage of the products used to date has been reduced by the use of hydrophilic, organically modified siloxanes. A product frequently used, for example by Sandvik among others, is Tegopren® 5863, sold by Evonik Goldschmidt GmbH. Tegopren® 5863 is water-soluble, and modified on the siloxane chain with two polyethers of different molar mass, both of which have the same content by mass of ethylene oxide, of about 40% ethylene oxide and about 60% propylene oxide. The product is applied in aqueous solution; the disadvantages of emulsion stability at relatively high temperature are eliminated. However, one disadvantage of this product class is that good separation of the melt granules does not remain constant, and it instead becomes somewhat more difficult as a function of time.
In addition, the shape of the melt granules can deviate slightly from the optimal spherical form. Bulging melt granules are obtained, among which flatter shaped bodies cause the described problems of the thinner edges breaking off and metering problems.
The solidified sulfur is frequently moved between production and reuse (transport, storage, handling, etc), and so preference is given to low evolution of dust and low propensity to fracture.